From 93a883fabffc23dcac75405bfb8f3df8042f9878 Mon Sep 17 00:00:00 2001 From: LagoLunatic Date: Mon, 24 Jun 2024 23:21:48 -0400 Subject: [PATCH] Document an obscure bug in J3DGDSetTexCoordScale2 --- src/JSystem/J3DGraphBase/J3DGD.cpp | 3 +++ 1 file changed, 3 insertions(+) diff --git a/src/JSystem/J3DGraphBase/J3DGD.cpp b/src/JSystem/J3DGraphBase/J3DGD.cpp index 985615134..5fc3ae450 100644 --- a/src/JSystem/J3DGraphBase/J3DGD.cpp +++ b/src/JSystem/J3DGraphBase/J3DGD.cpp @@ -278,6 +278,9 @@ void J3DGDSetTexCoordGen(GXTexGenType type, GXTexGenSrc src) { void J3DGDSetTexCoordScale2(GXTexCoordID id, u16 scaleS, u8 biasS, u8 wrapS, u16 scaleT, u8 biasT, u8 wrapT) { GDOverflowCheck(15); J3DGDWriteBPCmd(0xFE03FFFF); + // Bug: When id is GX_TEXCOORD_NULL (0xFF), the calculation below winds up producing the wrong + // BP register ID. Instead of a SU_SSIZE and SU_TSIZE register, it effectively negatively + // overflows to the previous registers: RAS1_TREF6 and RAS1_TREF7, potentially corrupting them. J3DGDWriteBPCmd((scaleS - 1) | (biasS << 16) | (wrapS << 17) | (0x30 + id * 2) << 24); J3DGDWriteBPCmd((scaleT - 1) | (biasT << 16) | (wrapT << 17) | (0x31 + id * 2) << 24); }